In a conventional motor-assisted power steering control device disclosed in, for instance, Japanese Patent Application No. 287008/1988, a control quantity for a motor has been obtained by summing a correction quantity obtained by the differentiation value of an error value between a target control torque and an actual steering torque, and a basic auxiliary steering force which is determined on the basis of a steering torque applied when the steering wheel is operated and a target control torque.
In the conventional control device, however, there was no compensation to phase lag for the control quantity which was obtained by summing a correction quantity obtained by the differentiation of an error quantity and the basic auxiliary steering force, as described above. Accordingly, there were problems of limitation in the response characteristic and a cause of fine vibrations of the steering wheel.